System and method for joining workpieces to form an article

ABSTRACT

A workpiece having at least one physical feature is placed into a workstation fixture having at least one adjustable locator. Measurement data reflecting the position of the at least one physical feature of the workpiece and measurement data reflecting the position of the at least one adjustable locator are obtained. A processor ingests and utilizes the collection of assembly data and the measurement data to define and store in memory at least one ordered pair correlating the physical feature and the adjustable locator. The processor defines a test vector that connects the position of the at least one physical feature and the position of the at least one adjustable locator. The processor to computationally discovers a best fit for adjusting the position of the adjustable locator to register with the physical feature by applying to the test vector a computational optimization process that seeks to minimize the length of the test vector to thereby generate a digital shim vector. The adjustable locator is then physically moved according to the digital shim vector, which is stored in association with the collection of assembly data.

FIELD

The present disclosure relates to a system and method for joining workpieces to form an article.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic illustration of an exemplary manufacturing system constructed in accordance with the teachings of the present disclosure;

FIG. 2 is a perspective view of a portion of the manufacturing system of FIG. 1, illustrating an exemplary positioning fixture constructed in accordance with the teachings of the present disclosure;

FIG. 3 is a schematic view depicting a portion of the positioning fixture of FIG. 2;

FIG. 4 is a schematic view depicting a portion of the positioning fixture of FIG. 2;

FIG. 5 is a schematic illustration of an exemplary process for joining workpieces in accordance with the teachings of the present disclosure;

FIG. 6 is a schematic illustration of an exemplary assembly that is formed of workpieces that are to be joined in a workstation of the manufacturing system of FIG. 1;

FIG. 7 is an enlarged portion of FIG. 6 that depicts a first orientation of selected features on a workpiece and a revised orientation of the selected features that is obtained through an optimization algorithm;

FIGS. 8 and 9 are schematic depictions of workpieces that are to be joined in the manufacturing system of FIG. 1, the workpieces being depicted as having independent and dependent relationships, respectively; and

FIG. 10 is a plot that depicts the propagation of variation in the fabrication of an article.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

With reference to FIG. 1 of the drawings, an exemplary system for manufacturing an article is generally indicated by reference numeral 10. The manufacturing system 10 can include a plurality of workstations that are employed to form one or more potions of the article from various workpieces. The workstations can be collectively or generally designated by reference numeral 12, or can be referred to specifically by reference numerals 12(a), 12(b), . . . 12(n−1) and 12(n). Each of the portions of the article can comprise two or more workpieces (e.g., W1, W2) that have been joined together in one of the workstations 12. In the particular example provided, the workpieces form a slip joint that is joined or secured by welding, but those of skill in the art will appreciate that each workstation 12 could employ one or more joining techniques, such as welding (e.g., arc-welding, MIG welding, TIG welding, spot welding, resistance welding), bonding, riveting, fastening, nailing, brazing, soldering, etc. Additionally, those of skill in the art will appreciate that the particular joint need not be a slip joint, but could be any type of joint, including a butt joint. Each workstation 12 can comprise a positioning fixture 20, a measuring device 22, and a workstation controller 24.

With reference to FIG. 2, each positioning fixture 20 can be configured to hold one or more workpieces (W1, W2) so that the joining process can be conducted in the workstation 12. The positioning fixture 20 can have a frame (jig) 30 and a plurality of locators 32 that are configured to position one or more of the workpieces relative to the frame 30.

Depending on the configuration of the workpieces that are to be joined in the workstation 12, the locators 32 can be configured in one or more sets. Generally speaking, one set of locators 32 can be employed to locate a first workpiece relative to the frame 30 and another set of locators 32 can be employed to locate a second workpiece relative to the frame 30. It will be understood, however, that one or more of the locators 32 in one set of locators 32 could be employed to position two or more workpieces relative to the frame 30. As will be discussed in more detail below, the locators 32 will include at least one primary locator 32 p. In some situations, a first workpiece can be positioned in a given workstation with a set of locators having no primary locators 32 p, and each workpiece that is to be joined to the first workpiece in the given workstation can be positioned with a set of locators having two primary locators 32 p. The locators 32 can be configured to engage one or more of the workpieces in a controlled manner to both locate the workpiece(s) in a desired manner and to eliminate translating movement along and rotational movement about X, Y and Z axes. One technique commonly employed in the design of positioning fixtures is referred to as the 3-2-1 principal of fixture design. Details regarding the design of such fixtures are beyond the scope of this disclosure, but briefly, the positioning fixture 20 is configured such that each workpiece:

a) rests on three non-collinear points on a bottom surface (i.e., in an X-Y plane), which fixes the location of the workpiece in a first direction along the Z-axis, rotationally about the Y-axis, and in a first rotational direction about the X-axis;

b) rests on two points on a side (X-Z plane), which fixes the location of the workpiece in one direction along the Y-axis and in a first rotational direction about the Z-axis; and

c) rests on one point on an adjacent surface (Y-Z plane) to fix the location of the workpiece in one direction along the X-axis and in a second rotational direction about the Z-axis.

Each locator 32 is disposed at a corresponding one of the points on which the workpiece rests. The locators 32 can comprise rest buttons or pads, concentric locators and radial locators. Clamps 38 can be employed to secure the workpiece to the positioning fixture 20 to thereby inhibit translation of the workpiece relative to the positioning fixture 20 along the X, Y and Z-axes, as well as rotationally about the X-axis in a second rotational direction.

If desired, the locators 32 can be movably coupled to the positioning fixture 20 so as to be capable of being used for the production of different finished articles. For example, the locators 32 could be positionable in a first orientiation to facilitate the joining of workpieces for a first finished article (e.g., the body-in-white of a sedan) and a second orientation to facilitate the joining of workpieces for a second finished article (e.g., the body-in-white of a sport-utility vehicle). The positioning of the locators 32 can be accomplished manually, or in an automated manner via an appropriate mechanism, such as one or more linear motors (not shown). Moreover, in situations where the locators 32 are moved in an automated manner, the positioning of the locators 32 can be controlled on an as-needed basis, so that workpieces for a variety of different finished articles could be processed together through the manufacturing system 10 (FIG. 1) without the need for significant down-time to re-tool the manufacturing system 10 (FIG. 1).

With reference to FIGS. 2 and 3, one or more of the locators 32, which can be a concentric locator or a radial locator, can be a primary locator 32 p. In the particular example provided, the primary locator 32 p is a concentric locator and comprises a pin 40, as well as first, second and third linear motors 42, 44 and 46, that are configured to translate the pin 40 along the X, Y and Z-axes, respectively, relative to the frame 30. As is schematically depicted in FIG. 3, the pin 40 can optionally be fixedly coupled the one or more other locators 32 in a given set of locators (i.e., a “first set of locators” in the particular example provided) so that operation of the first, second and third linear motors 42, 44 and 46 can optionally move all or a portion of the locators 32 in the particular set of locators (i.e., as a group) along the X, Y and Z-axes. The first, second, and third linear motors 42, 44 and 46 are depicted as employing jack- or ball-screws in the particular example provided, but it will be appreciated that any type of linear motor could be employed.

In some situations, the positioning fixture 20 can be configured to have a quantity of primary locators 32 p that is one less than the quantity of workpieces that are to be joined in the workstation 12, and each of the primary locators 32 p can be associated with a different set of locators. It will be appreciated, however, that the quantity of primary locators 32 p employed in a particular positioning fixture 20 can be varied as desired. For example, a single primary locator 32 p could be employed if movement of one type (e.g., translation along the X, Y and/or Z axes) was desired, while two primary locators 32 p could be if more than one type of movement (e.g., translation and rotation) was desired.

It will be appreciated that the purpose of the primary locators 32 p is to permit the set of locators 32 that control the positioning of one workpiece to be moved relative to the set of locators 32 that control the positioning of a second workpiece. Optionally, as shown in FIG. 4, the primary locator 32 p can include a pair of retractable clamping jaws 50 that are movable between a retracted position, which permits an associated workpiece W1 to be loaded onto the primary locator 32 p, and an extended position that can be employed to urge the workpiece W1 against a shoulder 52 or rest button to thereby fix the workpiece W1 against the shoulder 52 or rest button to inhibit translation along and rotation of the workpiece W1 about (the pin 40) of the primary locator 32 p.

Returning to FIG. 1, the measuring device 22 can be any type of device that is configured to collect data in real time relating to the physical positioning of various features on the workpieces when the workpieces are mounted on the positioning fixture 20 prior to the commencement of a joining operation. For example, the measuring device 22 can comprise a first device, such as a laser radar device or an optical measurement device, which is configured to collect 3-dimensional data relating to the workpieces, and an analyzing tool that can be employed to evaluate the 3-dimensional data and identify the size, shape and relative position of selected features on the workpieces. In the particular example provided, the analyzing tool employs data from the first device in conjunction with data transformation techniques and pattern recognition techniques to identify one or more of the selected features. Each of the features can comprise a surface or edge of a workpiece, a datum on a workpiece, a hole or slot in a workpiece, etc. and is selected for its ability to influence variation in the finished article. In the particular example provided, the analyzing tool is employed to a) determine the magnitude of variances between actual feature dimensions (size, location, etc.) and associated nominal feature dimensions (as determined from blueprints or CAD data), b) determine if any of the actual feature dimensions is out of tolerance, and c) statistically analyze the magnitude of the variances to determine if the actual feature dimensions are in statistical control or out of statistical control. The statistical analysis can be employed to identify instances where one or more features are being manufactured in a non-ideal manner so that corrective action can be implemented to ensure that workpieces subsequently fed into the manufacturing system 10 are less apt to add significant variation into the finished article. It will be appreciated that the non-ideal manner of manufacture could be the manufacture of the feature in an out-of-tolerance manner, or could be the positioning or forming of the feature at a position or to a size that deviates from its nominal blueprint location or size. Optionally, the measuring device 22 can be employed to identify features and/or components of the workpiece(s) and/or assembly that can be out-of-tolerance or otherwise non-conforming (e.g., incomplete or improperly assembled/fabricated) and generate an appropriate response, such as an alarm, flag or shut-down command, which can be used to prevent the out-of-tolerance/non-conforming workpiece or assembly from being used.

The workstation controller 24 can receive data and information from the measuring device 22 and can employ an optimizing algorithm to re-orient one or more of the workpieces relative to the other workpieces as desired. In this regard, the results of the optimizing algorithm can be employed to operate the first, second and third linear motors 42, 44 and 46 (FIG. 3) to move one or more of the locators 32 in a desired manner.

Generally speaking, the optimization algorithm can determine two vectors that can be employed to control the movement of a workpiece to an optimized location. The two vectors can include a first vector, which relates to rotation of the workpiece about an axis, and a second vector that relates to translation of the workpiece in a plane. It will be appreciated that the two vectors could be employed in separate movements (i.e., sequentially) or may be combined in some situations so that rotation and translation corrections could be implemented simultaneously. The optimization algorithm can also coordinate the movement of the primary locators 32 p for a given workpiece to prevent binding of a workpiece on a fixture or the breaking of one or more of the locators 32, and can perform a mapping function that identifies the (new) position of one or more of the features after the primary locator(s) 32 p have moved the workpiece(s).

With reference to FIGS. 5, a method for performing a joining operation at a given workstation 12 (FIG. 1) is schematically depicted. The method can begin at block 60, where a first workpiece and a second workpiece are mounted on first and second sets of locators 32 a and 32 b (FIG. 1), respectively. At this initial stage, each of the primary locators 32 p (FIG. 1) associated with the first set of locators 32 a (FIG. 1) is positioned relative to the second set of locators 32 b (FIG. 1) by an associated set of the first, second and third linear motors 42, 44 and 46 (FIG. 3) at an initial position. Clamps (not specifically shown) can be operated to secure the first and second workpieces to the frame 30 (FIG. 1).

The method can proceed to block 62, where the measuring device 22 (FIG. 1) can collect and analyze 3-dimensional data regarding selected features on the first and second workpieces. In the particular example shown in FIG. 6, which depicts a door D for an automotive vehicle, the features comprise first and second pairs of hinge mount holes HM1 and HM2, respectively, a pair of latch mount holes LM, and a datum line DL.

Returning to FIGS. 1 and 5, the method can proceed to decision block 64 where control (e.g., the workstation controller 24) can determine if the several features are in their optimized location. For purposes of this methodology, an optimized location of the features is the positioning of the first and second workpieces in a manner that minimizes the effect that the features of the first and second workpieces have on the magnitude of the variation in the fabrication of the article. Note that the optimized location of the features is not necessarily the location that minimizes the variation between the nominal location of each feature and the actual location of each feature, as in a least squares regression analysis. In our experience, the several features will have differing levels of influence on the magnitude of variation in the fabrication of the article and consequently, we employ a weighting technique in addition to advanced kinematics and engineering principals.

Referring to the example of FIG. 6, a hinge (not shown) that is to be mounted to the door D via the second pair of hinge mount holes HM2 and a latch (not shown) that is to be mounted to the door D via the pair of latch mount holes LM are configured with a relatively large degree of compliance (e.g., the holes in the hinge and the latch that receive fasteners that are threaded into the second hinge mount holes HM2 and latch mount holes LM are relatively larger in diameter than the fasteners), another hinge (not shown) that is to be mounted to the door D via the first pair of hinge mount holes HM1 is configured with a relatively smaller degree of compliance, and the datum line DL is critical to the gap-and flush fit of the door D to the remainder of the body (not shown) of the automotive vehicle. In this example, the datum line DL is given a first weight (e.g., a weight of one (1.0)), the first hinge mount holes HM1 is given a second, smaller weight (e.g., a weight of one-half (0.5)), while the second pair of hinge mount holes HM2 and the latch mount holes LM are each given still smaller weights (e.g., a weight of one-tenth (0.1)). Accordingly, the several features can be prioritized in the optimization algorithm such that the feature or features that most influence the magnitude of variation in the article can be oriented as close as possible to their nominal positions to thereby reduce the magnitude of variation in the article.

In some situations, the weighting could cause one or more of the features to be moved away or further away from their nominal position(s). In the example of FIG. 7, the latch mount holes LM are originally located at their nominal locations, but due to the priority associated with the location of the datum line DL, the workpiece W1 can be moved somewhat to re-orient the datum line (depicted in broken line), which can move the hinge mount holes HM (as shown in broken line) away from their nominal positions. In severe instances, one or more lower weighted features could actually be moved into a position that is actually considered out-of-tolerance but which nevertheless permits the first and second workpieces to be joined and functionally integrated into the article. For example, if second pair of hinge mount holes HM2 were to be positioned within +/−0.5 mm from their nominal position, but were positioned +0.6 mm from their nominal position due to the prioritization of the datum line DL, the optimization algorithm would permit the configuration if there was sufficient compliance between the hinge and the second pair of hinge mount holes HM2 to permit the door D to be mounted to the remainder of the vehicle body such that the door D opened, closed and latched properly and all criteria associated with the gap-and-flush fitting of the door D to the remainder of the vehicle body could be satisfied. One key to obtain the maximum benefit of the optimization algorithm is to appreciate that some tolerances may be somewhat arbitrary and that an out-of-tolerance situation for one feature does not necessarily render the article defective or inoperative. It will be appreciated, however, that limits could optionally be placed on the optimization algorithm that would not permit the location of one or more features to be positioned at an out-of-tolerance position.

With reference to FIGS. 8 and 9, another key to maximizing the benefit of the optimization algorithm concerns identifying or determining whether the workpieces that are to be joined are “independent”, which is shown in FIG. 8, or “dependent”, which is shown in FIG. 9. In both examples, two sets of locators (not specifically shown) are employed, with a first set of the locators being employed to position a first workpiece W1 and a second set of the locators being employed to position a second workpiece W2. In these situations only one primary locator (not shown) is required, but it will be appreciated that one or more additional primary locators could be integrated into the first set of locators and/or the second set of locators.

With reference to FIG. 8, an independent situation is depicted in which the features on one workpiece (e.g., the features Fa, Fb, Fc and Fd on the first workpiece W1) are able to be positioned relative to the features on a second workpiece (e.g., the features Fg, Fh, Fi, Fj and Fk on the second workpiece W2) without causing movement of the second workpiece W2. In the example provided, a portion of the first workpiece W1 overlies a portion of the second workpiece W2 and the two workpieces W1, W2 are joined together via a lap weld. The first workpiece W1 can be positioned independently of the second workpiece W2 so that the features Fa, Fb, Fc and Fd can be collectively oriented in a desired manner without movement of the second workpiece W2 or the features Fg, Fh, Fi, Fj and Fk.

With reference to FIG. 9, a dependent situation is depicted in which independent movement of the features on one workpiece (e.g., the features Fa, Fb, Fc, Fd, Fe and Ff on the first workpiece W1) relative to the features on a second workpiece (e.g., features Fg, Fh, Fi, Fj, Fk, Fl and Fm on the second workpiece W2) is limited by an interaction between at least one of the features on the first workpiece W1 and at least one of the features on the second workpiece W2. In the example provided, a portion of the first workpiece W1 overlies a portion of the second workpiece W2 and the first and second workpieces W1, W2 are secured to one another via a lap weld. Unlike the prior example, however, the features Fe and Ff on the first workpiece W1 and the features Fl and Fm on the second workpiece W2 are holes that are to be aligned to one another to receive threaded fasteners (not shown) therethrough that permit the joined first and second workpieces W1 and W2 to be mounted to a portion of the vehicle body. In this situation, movement of the first workpiece W1 relative to the second workpiece W2 is limited by a number of factors, including the amount of clearance between the holes and the threaded fasteners and the location of the holes in the vehicle body that receive the threaded fasteners.

Returning to FIGS. 1 and 5, if the features are not in their optimized locations, the method can proceed to block 66 where the primary locator 32 p (with the associated set of locators 32) can be moved by the first, second and third linear motors 42, 44 and 46 (FIG. 3) as required to position the first workpiece at a location that positions the features on the first and second workpieces at their optimized locations. The method can loop back to block 62, which permits the measuring device 22 to confirm the positioning of the features in their optimized locations (within predefined limits) and to permit the workstation controller 24 to confirm that the optimized locations have not changed.

Returning to decision block 64, if the features are in their optimized locations, the method can proceed to block 68 where the workpieces can be secured together. In the example provided, the workpieces are joined via a MIG welding process, but as noted above, other joining processes could be employed in the alternative. The method can proceed to block 70.

In block 70 the measuring device 22 can be employed to determine the locations of the features. The method can proceed to decision block 72.

In decision block 72, control determines whether the features are in their optimized locations within predefined tolerances. If the features are not in their optimized locations within the predefined tolerances, the method proceeds to block 74 where the assembly (i.e., the joined workpieces) are identified as being non-compliant. Such pieces may be scrapped or reworked as necessary.

Returning to decision block 72, if the features are in the optimized locations with the predefined tolerances, the method proceeds to bubble 76 where the method ends. The assembly is considered to be compliant with tolerances and can be fed into a subsequent workstation as part of the subsequent steps for fabricating the article. It will be appreciated that the positions of the primary locators 32 p can be returned to a “home” or “nominal position” after the joined assembly has been removed from the fixture. Optionally, the positions of the primary locators 32 p can be left at their current positions.

With reference to FIG. 10, a first plot P1 and a second plot P2 are employed to illustrate variation created in a prior art multi-step fabrication process and a multi-step fabrication process in accordance with the teachings of the present disclosure, respectively. A prior art system for fabricating an article is configured in a manner that seeks to position each pair of workpieces that are to be joined at predefined positions (e.g., their nominal positions) prior to the joining operation. Fabrication of the article in this manner produces variation (due to deviations in the tooling that is employed to fixture and orient the workpieces, as well as deviations in the workpieces themselves) that is compounded at each subsequent step of the fabrication process as depicted by the first plot P1 and as such, the magnitude of the variation that is possible in the finished article can be relatively large if there are many steps to the fabrication process and/or if the article is relatively complex in its configuration, such as a body-in-white. In contrast, the fabrication system of the present disclosure seeks to position each pair of workpieces that are to be joined in a manner that minimizes the magnitude of variation in article. In this regard, the several workpieces in a workstation can be positioned in optimized locations to eliminate variation caused by deviations in the tooling that is used to fixture and orient the workpieces, as well as to reduce variation caused by deviations in the workpieces themselves. Accordingly, variation created in one workstation can be attenuated in a subsequent station as shown in the second plot P2 and consequently, the magnitude of variation that is possible in the finished article is significantly reduced as compared to the prior art multi-step fabrication process.

It will be appreciated that the location optimizing technique that is employed in the workstations of the manufacturing system 10 (FIG. 1) can eliminate the effect of tooling wear on the fixturing that is used to position the workpieces, can eliminate the production of assemblies that are not fit for use in the finished article through real-time monitoring of the features of the workpieces before the joining operation, can reduce scrap by permitting the use of some workpieces having one or more out-of-tolerance features, and can improve the overall quality of the finished article relative to a conventional joining operation that seeks to orient workpieces in their nominal positions prior to joining the workpieces.

While the manufacturing system 10 (FIG. 1) has been described as employing a plurality of workstations 12 (FIG. 1), each having a positioning fixture 20 (FIG. 2) that includes a jig or a frame 30 (FIG. 2) and at least one primary locator 32 p (FIG. 2), it will be appreciated that a portion of the jig or frame 30 (FIG. 2) could be coupled to or integrated with a robot (i.e., the end effector of a robot) and the robot could be employed to vary the position of an associated workpiece in 3-dimensional space as needed. Configuration in this manner essentially integrates a set of the locators 32 (FIG. 2) with portion of the jig or frame 30 (FIG. 2) so that the motors that are employed to position the robot are substituted for the linear motors and move (as a group) the portion of the jig or fixture and an associated set of locators.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A method for fitting a workpiece to a workstation fixture having at least one adjustable locator, wherein the workpiece has at least one physical feature, the position of which is correlated to a collection of assembly data, the method comprising: placing the workpieces in the workstation; obtaining measurement data reflecting the position of the at least one physical feature of the workpiece; obtaining measurement data reflecting the position of the at least one adjustable locator; using a processor to ingest and utilize the collection of assembly data and the measurement data to define and store in memory at least one ordered pair correlating the at least one physical feature and the at least one adjustable locator; using the processor to define and store in memory, for the at least one ordered pair, a test vector that connects the position of the at least one physical feature and the position of the at least one adjustable locator, where the test vector has vector components represented as variables stored in memory; using the processor to computationally discover a best fit for adjusting the position of the at least one adjustable locator to register with the at least one physical feature by applying to the test vector a computational optimization process that seeks to minimize the length of the test vector to thereby generate a digital shim vector; causing the adjustable locator to physically move according to the digital shim vector to the calculated best fit position; and storing the digital shim vector in association with the collection of assembly data.
 2. The method of claim 1 wherein the step of causing the adjustable locator to move is performed using at least one motor or robot controlled by the processor.
 3. The method of claim 1 wherein the step of obtaining measurement data is performed optically while the workpieces are disposed in the workstation.
 4. The method of claim 1 wherein the step of obtaining measurement data is performed at least in part prior to placing at least one of the workpieces in the workstation.
 5. The method of claim 1 further comprising supplying said collection of assembly data as computer aided design data.
 6. The method of claim 1 wherein the computational optimization process employs a numerical optimization algorithm.
 7. The method of claim 1 wherein the computational optimization process employs a priority-based numerical optimization algorithm. 